With the development of high-power LED technology, the performance of LEDs for lighting applications has been improved significantly. Nowadays, the luminous efficacy of LED has achieved (70-90) lumens per watt (lm/W), much higher than that of the ordinary incandescent lamps. High power LEDs, have been widely used in lighting. It has been recognized as the fourth generation of lighting sources in the 21st century and which will eventually replace fluorescent lamps and incandescent lamps.
However, LED has high luminous efficiency and long life only when the temperature is below 80 degrees Celsius, so there are rigid requirements in the LED heat dissipation design. Poor heat dissipation causes light decay, low efficiency and short life. In order to achieve a good effect of heat dissipation and to replace the existing standard commercial lamps, U.S. Pat. No. 6,982,518 (Chinese Patent No. 1605790A, hereinafter “the '518 patent”) proposed a new LED lighting device.
The lighting device in the '518 patent includes a power supply converter, an optical engine utilizing a substrate with high heat conductivity, several LED semiconductor devices mechanically connected to the substrate, a peripheral bank fixed in the substrate and surrounding at least one part of the LED device, and a transparent polymer sealant set on the LED devices and confined by the periphery bank.
The heat dissipation system of the lighting device in the '518 patent uses solid materials (e.g. aluminum alloy, brass copper alloy, magnesium alloy, carbon polymer, carbon compounds of various metals and/or ceramic) with certain high thermal conductivity and stiffness to dissipate the heat from the LEDs and other devices. The structure of the heat dissipation system is finlike in order to dissipate a mass of heat by increasing the surface area of the heat dissipation. However, such a heat dissipation system has many drawbacks including heavy weight, excessive consumption of metal, complicated manufacturing process and high cost.
To solve the problems mentioned above, Chinese Patent No. 2735548 presented a heat dissipation structure for a high power LED, which comprises a shell base, a heat dissipation box, a circuit board and at least one high power LED. The heat dissipation box is sealed, containing some liquid for heat dissipation purpose. Due to the sound heat-conductivity of the liquid (with much lower thermal resistance than solid metals) in the sealed box, the thermal resistance between the heating elements and the cooling surface is reduced, which means that better effect can be achieved by using smaller heat dissipation surface area. However, the liquid for heat dissipation takes up considerable internal space, it adds not only the weight of the product but also the difficulty of installation, and the makes the product less safe.